System and method for navigating an ultrasound catheter to image a beating heart

ABSTRACT

Catheter navigation is coupled with ultrasound imaging to yield a context map showing the location on a heart of the ultrasonically imaged frame.

The present application is a continuation of U.S. patent applicationSer. No. 11/044,344, filed Jan. 27, 2005 which claims the benefit ofpriority to U.S. Provisional Patent Application No. 60/539,540, filedJan. 27, 2004 and which is a continuation-in-part of U.S. patentapplication Ser. No. 10/819,027, filed Apr. 6, 2004, which in turnclaims the benefit of priority to U.S. Provisional Patent Application60/461,004, filed Apr. 7, 2003 and is a continuation in part of U.S.patent application Ser. No. 09/107,371, filed Jun. 30, 1998. Eachapplication referenced in this paragraph is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention relates generally to a system and method fornavigating an ultrasound catheter to image a beating heart. Moreparticularly, the present invention relates to the coordination ofcatheter position data with ultrasound imaging data imaging a heart viaultrasound.

b. Background Art

Using ultrasound to image the interior of a beating heart is a knowntechnique. A series of patents (U.S. Pat. No. 5,345,940, issued Sep. 13,1994; U.S. Pat. No. 6,544,187, issued Apr. 8, 2003; U.S. Pat. No.5,713,363, issued Feb. 3, 1998) to Seward et al. describe theintra-cardiac ultrasound echo (ICE) technique and are incorporatedherein, in their entirety, by reference. According to this technique, anultrasonic transducer is situated at a distal end of a catheter that ispositioned in a heart chamber. The transducer vibrates in response to acontrol signal to generate an ultrasonic wave. The transducer senses thereflected wave and transmits the corresponding signal to transceivercircuitry that analyzes the incoming signal and generates an imagesignal that is shown on a display. In this manner, a user can see, on amonitor, a real-time image of a small portion of the interior surface ofthe heart. Repositioning or reorienting the catheter, such that thetransducer's wave bounces off a different portion of the surface, willyield a new image.

The ICE technique has lacked the ability to link the ultrasoundinformation with other clinical information such as cardiacelectrographic data anatomic orientation of the ultrasound data orimages.

Further, Wittkampf, in a series of patents (U.S. Pat. No. 5,983,126,issued Nov. 9, 1999; U.S. Pat. No. 5,697,377, issued Dec. 16, 1997),describes the application of orthogonal current pulses to an electrodearrangement on a catheter to yield three-dimensional position data toassist a user in navigating the catheter. More specifically, in theWittkampf system, current pulses are applied to orthogonally placedpatch electrodes placed on the surface of the patient. These patches areused to create specific electric fields inside the patient. TheWittkampf patents teach the delivery of small-amplitude low-currentpulses supplied continuously at three different frequencies, one on eachaxis. Any measurement electrode placed in these electric fieldsexperience a voltage that depends on its location between the variouspatches or surface electrodes on each axis. The voltage on themeasurement electrode in the field when referred to a stable positionalreference electrode indicates the position of the measurement electrodewith respect to that reference. The three voltages give rise to alocation of the measurement electrode in “three space”.

Co-pending application Ser. No. 10/819,027 describes the application ofthe Wittkampf technique, with improvements, to locate a catheterpositioned in the interior of the heart and to image a catheter in realtime. Further, application Ser. No. 10/819,027 describes how tosequentially use locations of an electrode in contact with the heartwall to sequentially build a model of a heart chamber.

Devices and techniques are known for determining the location in spaceand the orientation of the tip of a catheter. A series of patents toDesai (U.S. Pat. No. 5,215,103, issued Jun. 1, 1993; U.S. Pat. No.5,231,995, issued Aug. 3, 1993; U.S. Pat. No. 5,397,339, issued Mar. 14,1995; U.S. Pat. No. 4,940,064, issued Jul. 10, 1990; and U.S. Pat. No.5,500,011, issued Mar. 19, 1996), incorporated herein by reference intheir entirety, describes an electrode array arrangement located on acatheter that can be used to determine the location of the catheter tipusing Wittkampfs technique.

What has been needed is a device and method for producing images of theinterior of a heart via ultrasound coupled with a navigational systemfor allowing the user to see what portion of the heart is appearing onthe ultrasound image. Further, what has been needed is a method forbuilding a geometry of the heart by successively imaging portions of theheart surface, with successive images being framed based the location ofthe frames previously taken and by corresponding manipulation of theimaging device to select a new frame.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a convenient,easy-to-use system and method for ultrasonically imaging a desiredportion of a beating heart.

Another object of the present invention is to provide a system foridentifying, on a context map, the location of an image obtained of aninterior surface of a beating heart via ultrasound.

Yet another object of the present invention is to build a model of aheart chamber through sequential ultrasound imaging with collection andcalculation of position and orientation data.

Still another object of the present invention is to allow easy updatingor elucidation of important heart structure after a working model of theheart is constructed.

Another object of the invention is to build a geometry of a beatingheart without touching the endocardial wall with a probe.

Yet another object of the present invention is to provide a system toprovide lower cost transseptal puncture procedures using a smallercatheter than is typically used for ICE.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary version of a system for navigating an ultrasound transduceris shown in the figures wherein like reference numerals refer toequivalent structure throughout, and wherein:

FIG. 1 is a schematic representation of a system for navigating anultrasound transducer;

FIG. 2 is a partial view of the system of FIG. 1, with an electrodearray in a deployed configuration and with ultrasound waves and echosdepicted;

FIGS. 3 a, b, c are prior art depictions of an electrode array that isemployed in the system of FIGS. 1 and 2;

FIG. 4 a is a schematic illustration of an image of heart geometry andan ultrasonic image generated by the system 1 taken at a first frame;and

FIG. 4 b is a schematic illustration of an image of heart geometry andan ultrasonic image generated by the system 1 taken at a second frame;and

FIG. 5 is a flow chart depicted a method of using the system of FIG. 1to generate a geometry of the heart.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a cardiac imaging and navigation system 1 that coordinatesan ultrasonic data acquisition and imaging system 2 with a catheternavigation system 3. The system 1 produces an ultrasonic image 4 of theheart 5 and displays a context or reference map 6 of the heartindicating the portion of the heart 5 that appears in the ultrasonicimage frame 4. In a preferred use, the system 1 observes a beating heart5. The navigation system 1 includes a catheter system 10 electronicallylinked to a signal processing system 11 that in turn is electronicallylinked to an image display system 12. In one embodiment, theseelectronic linkages are made via wire connections. In other embodiments,wireless links may be used for data transfer.

A preferred catheter system 10 is illustrated in FIGS. 1 and 2. Thecatheter system 10 includes a guide tube 15 that is somewhat flexible sothat in use it can easily pass through a patient's cardiovascularstructures. In use, the catheter's distal end or tip 16 can bepositioned within a heart chamber 20 defined by a chamber wall 21, asshown in FIGS. 1 and 2.

Proximate the distal end 16 of the catheter system 10, is an ultrasonictransducer 25 that includes a crystal or array of crystals for sendingand sensing ultrasonic waves. The transducer 25 is electronically linkedto a dedicated ultrasound processor 26 having or linked to transceivercircuitry 26 a, control circuitry 26 b and imaging circuitry 26 c. Viathe transceiver 26 a, the ultrasound processor 26 triggers a vibrationin the ultrasonic transducer 25 that in turn imparts an sound wave 27(FIG. 2) to the surrounding blood in the heart chamber 20. The wave 27propagates through the blood in a direction determined or calculablefrom the known position and orientation of the crystals in thetransducer 25. The wave 27 “bounces” against the chamber wall 20. Aportion 28 of the wave 27 is reflected by the chamber wall 20 andreturns to the transducer 25. The transducer 25 senses the returned wave28 and sends a signal to the ultrasound processor 26. The ultrasoundprocessor 26 has data storage and processing functions that calculatethe distance “D” between the transducer and the heart wall 21, using thetime of travel (t) of the wave 27 through the blood pool that has aknown density. In addition, the reflected wave 28 signal is used by theimaging circuitry 26 c to generate an image 4 that is displayed on ascreen or monitor 28. This frame 29 of the image 4 is typicallyrelatively small (on the order of a few millimeters by a fewmillimeters) due to the size of the ultrasonic transducer 25 (i.e. thediameter and arrangement of the crystals in the transducer 25) whichmust be of a small scale to be used in intracardiac applications.

To aid the user in interpreting the ultrasound image 4, the presentsystem 1 employs a catheter navigation system 3 as illustrated in FIGS.1 and 2. This navigation system 3 determines the location in space andthe orientation of the catheter distal end 16 and is thereby able tohighlight or indicate on a context map 6 what portion of the heart wall21 is displayed in the ultrasound image 4. Read together, the ultrasoundimage 4 and the highlighted context map 6 give the user information toposition the catheter 12 in a desired location to view pertinent areasof the heart 5. In addition, the coordination of the image 4 and thehighlighted context map 6 allow the user to manipulate the catheter tosequentially capture a number of image frames to generate a geometry ofa larger portion of the heart or of the whole heart.

Various techniques have been proposed to carry out measurements ofcatheter location. Although the various techniques differ in detail,most systems involve the generation of a non-ionizing field in the heartand the detection of a catheter element within the field. The source ofthe field may be exterior of the patient or may be created within theheart itself with an appropriate catheter system. However, all of thesetechniques generate a set of points having locations in physical space.Suitable techniques are known from the incorporate references and U.S.Pat. No. 5,697,377 to Wittkampf. A generated field creates a detectablesignal at a sensor element on the catheter. The nature of the fielddictates the sensor element. Electrical fields may be detected byelectrodes, while magnetic fields may be detected by magnetic sensors.

In greater detail, the illustrated embodiment of a catheter navigationsystem 3 includes a sensor electrode array 35 proximate the distal end16 of the catheter tube 15. The electrode array 35 preferably includes asmall collection of spaced sensor electrodes 40, 42, 44, 46, 48, thatare deployed such that they are spaced from one another sufficiently toyield accurate position and orientation data when exposed to orthogonalcurrents as taught by Wittkampf. An example of an electrode array 35configuration that achieves this objective is that disclosed by Desai inthe patents discussed above, and incorporated herein by reference, inthe Background section. The Desai configuration is illustrated in FIGS.3A-3C. and is characterized by a plurality of side sensor electrodes 42,44, 46, 48 equally spaced around the distal end 16 of a tubular catheter15. A further, central electrode 40 is fixed to the distal end 16 on thecatheter axis 50. The four side electrodes 42, 44, 46, 48 lie in thesame plane 52 (FIG. 2) and are equally spaced from adjacent electrodes.The side electrodes 42, 44, 46, 48 are at the apexes of a square patternwith the central electrode 40 in the center of the square. Theelectrodes may be made of highly electrically conductive material. Aplurality of longitudinally directed slits, as exemplified by slits 55and 56, are cut through the tube 15 from a point adjacent to theterminating end 60 to a distance away from the terminating end 60. Theslits 55, 56 define and form intermediate limbs 62, 63, 64, 65. Theelectrodes 42, 44, 46, 48 are positioned with one electrode to a limb62, 63, 64 or 65. By applying a compressive force to the end 60, thelimbs 62-65 buckle, thereby spreading the side electrodes 42, 44, 46, 48apart, as illustrated in FIG. 3C.

Alternative electrode arrangements are contemplated. An arrangement withat least two electrodes can provide position and orientation data,though increasing the number and spacing of electrodes yields a higherdegree of accuracy.

FIG. 1 illustrates additional elements of the navigation system 3.External patch electrodes 70, 71, 72, 73 are placed on the patient,directed substantially near the heart. The electrodes 70-73 areelectrically connected to navigation circuitry 80 which impartscontrolled current in a desired fashion to the electrodes 70-73. Thenavigation circuitry 80 is also electronically connected to the sensorelectrodes 40, 42, 44, 46, 48 (as depicted by arrow 75) and receives andprocesses signals from the sensing electrodes 40, 42, 44, 46, 48.

According to the techniques described by Wittkampf in the patents notedabove in the Background section and incorporated herein by reference,the navigation circuitry 80 imparts orthogonal current signals throughthe patient. Each of the signals has a respective characteristic thatrenders it distinguishable from the other orthogonal signals. Inresponse to the field generated by this current, the sensing electrodes40, 42, 44, 46, 48 send voltage signals to the navigation circuitry 80.The navigation circuitry 80 processes this signal information in themanner described in pending U.S. patent application Ser. No. 10/819,027to determine the location of the catheter distal end 16, as well as theorientation of the catheter tube 15 as defined by the vector “R” (FIG.2) extending axially from the end 16 of the catheter tube 15.

In a preferred embodiment the navigation circuitry 80 is linked for datatransfer (as depicted by arrow 82) to a computer system 90 having a userinterface to allow control of the navigation circuitry. In addition, ina preferred embodiment, the ultrasound processor 26 is linked for datatransfer (as depicted by arrow 92) to a computer system 90 having a userinterface to allow control of the ultrasound processor. Most preferably,the navigation circuitry 80 and the ultrasound processor are linked to asingle computer that coordinates the operation of the imaging being doneby the ultrasound system 2 with the navigation system 3.

The navigation circuitry 80 is linked for data transfer (as depicted byarrow 94) to a display screen or monitor 100. Similarly, the ultrasoundprocessor 26 is linked for data transfer (as depicted by arrow 96) to ascreen or monitor 102. The navigation circuitry 90 generates a contextmap 6 of the whole heart 5 or of a relatively large section of the heart5 with an indication thereon of the location of the catheter distal end16. More specifically, the computer system 90, with processingcapabilities, coordinates the position and orientation data from thenavigation system 3 with the distance-to-wall data received from theultrasound system 2 to compute and illustrate, on monitor 100, thelocation on the heart of the frame 4 that is simultaneously displayed onan ultrasound image display screen or monitor 102. In this manner, thehighlighted or animated region 105 of the context map 6 depicts theportion or frame of the heart wall at which the ultrasound is “pointed”.In one embodiment, monitors 100 and 102 are separate screens; inalternate embodiments, both images (the context map 6 and the ultrasoundimage 4) are depicted on one monitor. The process of capturingultrasound data and making the locating calculations occurs fast enoughthat the distance data can be used to computer motion data if desired.

FIG. 4 further illustrates the relationship between the context map 6and the ultrasound image frame 4: the highlighted region 105 of thecontext map 6 indicates the location in the heart of the ultrasoundimage frame 4. The context map 6 presents a wider field of view than isshown by the ultrasound image frame 4, and the context map 6 includesthe frame 4 shown by the ultrasound image. This relationship between therelatively small field of view shown by the ultrasound frame 4 and therelatively larger field of view (including the frame 4) shown by thecontext map 6 is suggested by projection lines 110, 111.

The system 1 can be used to generate a geometry of the heart throughiterative ultrasound imaging made feasible through the manipulation ofthe catheter system 10 using the navigation system 3 for guidance. FIG.5 is a flow chart depicting the steps in the iterative process 200. Theuser positions (205) the catheter system 10 in the chamber of the heart5. As depicted in step 210, electric potentials are applied toelectrodes 70-73 and this potential is sensed by electrodes 40, 42, 44,46, 48. Using Wittkampfs method, the 3D positions of each senseelectrode 40, 42, 44, 46, 48 are determined and displayed. In addition,an orientation vector R is determined. Because the ultrasound crystal isin a known fixed location in relation to the catheter head 60, thelocation (Lxtal) of the ultrasound crystal is determined.

At essentially the same time, the ultrasound system 2 emits and senses asound wave. The distance D to the heart wall 21 is calculated as D=Vb*t,where Vb is the apriori known velocity of the ultrasound signal in bloodand t is the time measured from issuing the pulse to sensing thereturned echo 28. This ultrasound process is indicated by block 215.

Applying the position data from step 210 and the ultrasound data fromstep 215, the location of a frame or patch 4 of the wall is calculated(220). The ultrasound data is stored in association with the locationand orientation data. The location Lw of the center of the patch orframe 4 is calculated as follows: Lw=Lxstal+D*R. This location islocated in relation to the catheter (Lw); in addition, the x, y, zcoordinates of the wall patch in space can be calculated and stored,since the 3D position and orientation of the transducer 25 is known,along with the distance D to the wall.

A graphic rendering 105 of the patch or frame 4 is created (225) on ascreen or monitor 100.

As indicated by decision block 230, if the view of the single frame 4 issufficient for the user's purposes (235), the process may end here(240). However, if the user has not viewed the site of interest in full(242), the user may, based upon the graphic image in the context map 6,“build” a geometry of a larger portion of the heart, or of the wholeheart, by iteratively or sequentially imaging different frames (whichmay or may not overlap) of the heart, with the system 1 collecting andstoring position and orientation data in association with the ultrasounddata for each such frame. To move from frame to frame, the usermanipulates the catheter system 10 to change the orientation R of thecatheter system 10 or to move the catheter system 10 to a new positionwithin the heart 5, such that the ultrasound system “points at” anddisplays a different frame or patch 4′. This repositioning step isindicated at reference number 245. Thereafter, the position determiningstep 210, the ultrasound step 215, the calculation step 220 and thegraphic rendering step 225 and the decision step 230 are repeated untilthe resulting geometry of the heart is sufficient (235) for the user'spurposes. The completed geometry is displayed (250). Positioning andorientation of the catheter system 10 may be accomplished manually.Alternatively, the catheter system is coupled to a robotic mechanismcontrolled, for example, by the computer 90, to position and orient thecatheter.

FIG. 4 b shows the how the context map 6′ appears with the ultrasoundsystem 2 trained on a second patch or frame 105′. The first frame 105 isindicated for reference with broken lines in the drawing of FIG. 4 b; itmay or may not be indicated in some manner on the context map 6′ shownon the monitor 100. FIG. 4 b also shows the relationship between theframe 105′ on the context map 6′ to the ultrasound frame 4′ shown on theultrasound image monitor 102.

The system 1 of the present invention offers advantage over traditionalICE, where a large number of crystals in the transducer are necessary toachieve the desired image quality, because with the present inventionallows for a smaller number of crystals to achieve a comparable level ofperformance, because it has the ability to signal average the acquireddata. This is possible because the ultrasound data is acquired from aknown location. Combining this knowledge with cardiac gating, multipleacquisitions from a site may be averaged.

Another advantage of the present invention with a smaller number ofcrystals over traditional ICE is that the head of the catheter may beforward-looking, i.e. the wave 27 propagated by the transducer 25travels in a direction R that is generally parallel to the axis 50 ofthe catheter 10. Traditional ICE catheters, like those shown by Seward,“look” off to the side of the catheter and therefore are somewhat moredifficult to operate.

Yet another advantage is that the catheter system 10, having a customarysize and flexibility and being equipped with electrodes, may be used asa standard cardiac electrophysiology mapping catheter.

Although an illustrative version of the device is shown, it should beclear that many modifications to the device may be made withoutdeparting from the scope of the invention.

1. A system for navigating an ultrasound catheter to image a beatingheart, comprising: a catheter carrying an ultrasonic transducerconfigured to generate a sound wave and sense an echo wave to obtainultrasound data for a first portion of the interior surface of theheart; and, an imaging system for simultaneously displaying anultrasound image of the first portion and a three-dimensional contextmap of the heart and simultaneously highlighting a first surface on thecontext map corresponding to the first portion and a second surface onthe context map corresponding to a second portion of the interiorsurface of the heart for which ultrasound data was previously capturedby the ultrasonic transducer.
 2. The system of claim 1 wherein theimaging system displays the ultrasound image in real time.
 3. The systemof claim 1 wherein the first and second portions partially overlap. 4.The system of claim 1 wherein the context map displays a section of theheart that includes the first portion and additional portions of theheart adjacent the first portion.
 5. The system of claim 1, furthercomprising a robotic mechanism operatively coupled to the catheter toposition and orient the catheter.
 6. A system for navigating anultrasound catheter to image a beating heart, comprising: a cathetercarrying a sensor element and an ultrasonic transducer configured togenerate a sound wave and sense an echo wave to obtain ultrasound datafor a first portion of the interior surface of the heart; a navigationsystem operatively coupled to the sensor element for determining aposition of the first portion; and, an imaging system for simultaneouslydisplaying an ultrasound image of the first portion and athree-dimensional context map of the heart and simultaneouslyhighlighting a first surface on the context map corresponding to thefirst portion and a second surface on the context map corresponding to asecond portion of the interior surface of the heart for which ultrasounddata was previously captured by the ultrasonic transducer.
 7. The systemof claim 6, wherein said navigation system determines a position and anorientation of the sensor element.
 8. The system of claim 6 wherein saidsensor element is disposed on a longitudinal axis of the catheter andthe catheter includes a plurality of additional sensor elements, eachone of the additional sensor elements spaced radially from the axis andat approximately equal circumferential distances from circumferentiallyadjacent others of the additional sensor elements.
 9. The system ofclaim 6 wherein said additional sensor elements are in a common plane.10. The system of claim 1 wherein the position of the first portion isdetermined responsive to a position of the sensor element and theultrasound data.
 11. The system of claim 6 wherein the imaging systemdisplays the ultrasound image in real time.
 12. The system of claim 6wherein the first and second portions partially overlap.
 13. The systemof claim 6 wherein the context map displays a section of the heart thatincludes the first portion and additional portions of the heart adjacentthe first portion.
 14. The system of claim 6, further comprising arobotic mechanism operatively coupled to the catheter to position andorient the catheter.
 15. A method of navigating an ultrasound catheterto image a beating heart, comprising the steps of: positioning acatheter in the interior of the heart, the catheter carrying anultrasonic transducer; generating a sound wave and sensing an echo waveto obtain ultrasound data for a first portion of the interior surface ofthe heart; and, simultaneously displaying an ultrasound image of thefirst portion and a three-dimensional context map of the heart andsimultaneously highlighting a first surface on the context mapcorresponding to the first portion and a second surface on the contextmap corresponding to a second portion on the interior surface of theheart for which ultrasound data was previously captured by theultrasonic transducer.
 16. The method of claim 15 wherein said catheterfurther carries a sensor element and further comprising the step ofdetermining a position of the sensor element.
 17. The method of claim16, further comprising the steps of: determining a position of theultrasonic transducer responsive to the position of the sensor element;calculating a distance from the ultrasonic transducer to the firstportion; and, determining a location of the first portion responsive tothe position of the ultrasonic transducer and the distance.
 18. Themethod of claim 15, further comprising the steps of repositioning thecatheter in the interior of the heart; generating a sound wave andsensing an echo wave to obtain ultrasound data for a third portion ofthe interior surface of the heart; and, simultaneously displaying anultrasound image of the third portion and a three-dimensional contextmap of the heart and simultaneously highlighting the first and secondsurfaces and a third surface on the context map corresponding to thethird portion.
 19. The method of claim 15 wherein the ultrasound imageis displayed in real time.
 20. The method of claim 15 wherein the firstand second portions partially overlap.